Two-dimensional semiconductors have excellent electrical, mechanical, and optical properties and thus are drawing a lot of attention as next-generation semiconductor materials which can be applied to flexible devices and transparent devices.
In this regard, Korean Patent No. 10-1251340 (entitled “Light emitting diode and manufacturing method of the same”) discloses a semiconductor light emitting diode and a method of manufacturing the semiconductor light emitting diode in which a two-dimensional photonic crystal pattern is formed in an interface of a transparent electrode layer with a p-type semiconductor layer, so that light extraction efficiency can be improved, and a contact area between the p-type semiconductor layer and the transparent electrode layer is reduced, so that conducting properties of the semiconductor light emitting diode can be improved.
In a process of manufacturing an electronic device using a two-dimensional semiconductor material, a method of forming an electrode on a two-dimensional semiconductor is very important because a contact resistance between the two-dimensional semiconductor and the electrode varies depending on the method used.
That is, the contact resistance between the two-dimensional semiconductor and the electrode highly affects the performance of the device. Therefore, a method of reducing the contact resistance between the two-dimensional semiconductor and the electrode is becoming an issue.
Conventionally, the contact resistance between the two-dimensional semiconductor and the electrode has been reduced by changing properties of the electrode or brining the electrode into contact with an edge of the two-dimensional semiconductor.
Specifically, according to a method of reducing the contact resistance by changing properties of the electrode, a change in density of states of the two-dimensional semiconductor is caused by physical or chemical adsorption between the electrode and the two-dimensional semiconductor in contact with the electrode depending on properties of the electrode. Meanwhile, metal which is a three-dimensional material has a sufficient amount of charges (electrons/holes) to be transferred to a semiconductor layer, whereas a two-dimensional semiconductor material is limited in space to receive charges transferred from metal and thus has a high contact resistance. Further, the two-dimensional semiconductor material does not include a dangling bond on its surface. Therefore, if the two-dimensional semiconductor material is bonded to a metal electrode, atomic combination does not occur but a Van Der Waals gap is formed therebetween, so that it is difficult to transfer charges from the electrode to the semiconductor layer. As such, there is insufficient space to receive charges in the two-dimensional semiconductor and it is difficult for charges to be transferred due to the Van Der Waals gap, which causes a high contact resistance. Further, a large-scale two-dimensional semiconductor can be present as a p-type semiconductor in the air. In this case, if metal commonly used as an electrode material is brought into contact with the two-dimensional semiconductor, the two-dimensional semiconductor is doped into an n-type semiconductor. Therefore, when the metal electrode is brought into contact with the two-dimensional semiconductor, a density of states is reduced, so that a contact resistance may be increased.
Further, according to a method of reducing the contact resistance by bringing the electrode into contact with an edge of the two-dimensional semiconductor, the contact resistance can be reduced by increasing a path for charges to move from the electrode to a two-dimensional semiconductor material. However, in order to form the electrode on the edge of the two-dimensional semiconductor, the edge of the two-dimensional semiconductor and the electrode need to be aligned.
Accordingly, there is a need for a new method of forming an electrode for reducing the contact resistance between the two-dimensional semiconductor and the electrode in the process of manufacturing an electronic device using the two-dimensional semiconductor.